The invention relates to the field of biopsy devices.
A needle biopsy device is frequently used to obtain a piece of tissue for microscopic examination to determine malignancy, while subjecting the patient to the least trauma. Typically, the instrument consists of a long, thin, probe, termed a stylet, within a close-fitting hollow needle, termed a cannula. The stylet and cannula are controlled manually or by a firing mechanism that first projects the stylet into a tissue mass, followed by the cannula. The stylet has a notch into which tissue will prolapse when the stylet penetrates the tissue mass. As the cannula slides over the stylet, a small piece of tissue is severed from the tissue mass and captured within the notch of the stylet. The device is then withdrawn and the piece of tissue removed from the stylet notch. An example of a device including a two-stage actuation mechanism in which the cutting needle and cannula are advanced in timed sequence under spring actuation is described in Bates, U.S. Pat. No. 4,958,625, the entire contents of which is incorporated herein by reference.